Omni-directional cameras (may also be said to be “all-around view camera”) can acquire images in a wide range of field of view using a single camera, and are therefore used in a variety of fields. Omni-directional cameras are used, for example, for a monitoring system. Omni-directional cameras can acquire omni-directional images using an all-around view lens optical system such as a fish-eye lens or an all-around view mirror optical system such as a spherical mirror.
There are various display modes of an omni-directional image acquired using an omni-directional camera such as a mode in which an omni-directional image is displayed developed into a panoramic image and a mode in which a region including a target object is extracted from an onmi-directional image and displayed. In the mode in which a region including a target object is extracted from an omni-directional image and displayed, a user designates an extraction position from the omni-directional image, and the image at the designated position is subjected to distortion correction processing and displayed on a monitor. Note that when an omni-directional image is displayed, the image is generally subjected to distortion correction.
Here, PTL 1 discloses a display method and an apparatus that allow a user to intuitively designate a desired extraction position from an image obtained by an omni-directional camera. More specifically, an omni-directional image is subjected to coordinate transformation and displayed on a monitor so that the x-axis and y-axis which are orthogonal to each other on an actual plane (in the omni-directional image, these x-axis and y-axis are not orthogonal to each other) are also orthogonal to each other on the display monitor. Actually, a plan map in which the actual x-axis and y-axis are orthogonal to each other is set, pixels of the omni-directional image are subjected to coordinate transformation so as to correspond to each position on the plan map and displayed on the plan map (hereinafter, an image transformed into coordinates on the plan map and displayed will be referred to as “map image”).
By so doing, it is possible to display an omni-directional image whose positional relationship is easy to understand on the plan map and intuitively select an extraction position as well.